The present invention relates to a copper foil excellent in laser punchability with which an copper layer connection hole (through hole and via hole) of a printed circuit board can efficiently be formed and also relates to a method for manufacturing such a copper foil.
The copper foil of the present invention includes not only a copper foil alone but also all kinds of copper-laminated boards and build-up laminated board on which copper is directly formed (including electroplated and electroless plated ones)
A drill has been employed for forming a small diameter hole (through hole) for copper layer connection of a printed circuit board. Since burrs have easily been formed in the processing (forming holes) by a drill and opening of a hole with an ultra small diameter has been limited, however, a method for forming a hole by laser has been employed recently.
However, a copper foil has a disadvantageous point that the surface of the copper foil conventionally employed for a printed circuit board has a high reflectance to result in inferior processibility with laser beams. Therefore, a method for forming a hole by removing a prescribed copper foil part by etching and then forming a hole by radiating laser beams to the part or a method for forming a hole by thinning a copper foil by chemical polishing and then processing with laser beams have been employed.
In these cases, however, since a step of removing a copper foil by etching or of chemical processing is employed, efficiency has been deteriorated and also since strict control is required for operation of such processing procedures, productivity is lowered and the cost is heightened.
The present invention has been achieved while taking the foregoing problems into consideration. The purposes of the present invention are to provide a copper foil excellent in drilling property by laser and suitable for forming through hole and via hole with a small diameter and also to provide a method for manufacturing such a copper foil by improving the surface of a copper foil at the time of manufacturing a printed circuit board.
As described above, the present invention provides the following copper foils:
1. A copper foil excellent in drilling property by laser, having a layer containing any one or more substances selected from indium, tin, cobalt, zinc, cobalt alloys, and nickel alloys on the face to be radiated with laser beams;
2. a copper foil excellent in drilling property by laser as set forth in the above described item 1, having cobalt alloys layer containing at least one of nickel, phosphorus, zinc and copper;
3. a copper foil excellent in drilling property by laser as set forth in the above described item 1, having nickel alloys layer containing at least one of copper, zinc, and phosphorus;
4. a copper foil excellent in drilling property by laser as respectively set forth in the above described items 1 to 3, in which content of cobalt, nickel, tin, zinc, or indium is independently 0.1 to 100 mg/dm2 (provided that, zinc content is 0.5 to 100 mg/dm2); and
5. a copper foil excellent in drilling property by laser as respectively set forth in the above described items 1 to 4, in which thickness of the copper foil is 18 xcexcm or thinner.
The present invention further provides the following methods for manufacturing a copper foil excellent in drilling property by laser:
6. A method for manufacturing a copper foil excellent in drilling property by laser, in which a layer containing any one or more substances selected from indium, tin, cobalt, zinc, cobalt alloys, and nickel alloys is formed on the face to be radiated with laser beams;
7. a method for manufacturing a copper foil excellent in drilling property by laser as set forth in the above described item 6, in which cobalt alloys layer containing at least one of nickel, phosphorus, zinc and copper is formed;
8. a method for manufacturing a copper foil excellent in drilling property by laser as set forth in the above described item 6, in which nickel alloys layer containing at least one of copper, zinc, and phosphorus is formed;
9. a method for manufacturing a copper foil excellent in drilling property by laser as respectively set forth in the above described items 6 to 8, in which the layer is formed by plating;
10. a method for manufacturing a copper foil excellent in drilling property by laser as respectively set forth in the above described items 6 to 9, in which content of cobalt, nickel, tin, zinc, or indium is independently 0.1 to 100 mg/dm2 (provided that zinc content is 0.5 to 100 mg/dm2);
11. a method for manufacturing a copper foil excellent in drilling property by laser as respectively set forth in the above described items 6 to 10, in which thickness of the copper foil is 18 xcexcm or thinner;
12. a method for manufacturing a copper foil excellent in drilling property by laser as respectively set forth in the above described items 6 to 11, in which stabilizer treatment is carried out after the layer formation; and
13. a method for manufacturing a copper foil excellent in drilling property by laser as set forth in the above described item 12, in which the surface treated by the stabilizer treatment contains chromium and/or zinc.
The present invention includes formation of a layer containing any one or more of substances selected from indium, tin, cobalt, zinc, cobalt alloys and nickel alloys in a position of a copper foil of a printed circuit board where through hole and via hole is to be formed by radiating laser beams thereto, and thereby drilling property by laser is significantly improved as compared with that of a conventional copper foil.
A copper foil used in the present invention may be an electrodeposited copper foil and a rolled copper foil. Further, the thickness of the copper foil is desirably 18 xcexcm or thinner for the use in high density wiring.
Nevertheless, the thickness of a copper foil of the present invention with improved laser drilling property is not necessarily restricted within the defined thickness and may, of course, be thicker than the defined thickness.
A layer containing any one or more of substances selected from indium, tin, cobalt, zinc, cobalt alloys and nickel alloys is formed on the face of a copper foil to which laser beams is radiated.
Such a layer can be produced by plating treatment. However, the method is not limited to plating, but vapor deposition, sputtering, or other coating methods may be employed for the layer formation.
Further, even in the case plating treatment is employed, the plating treatment method is not at all restricted to a specified plating method. The layer formation by such a plating method can be carried out either partly on the face of a copper foil to be radiated with laser beams thereto or fully on the copper foil. Such a plating treatment is naturally required to be carried out without deteriorating the characteristic properties of a copper foil usable for a circuit board and any treatment of the present invention sufficiently satisfies such conditions.
In the foregoing alloy layers to be formed on a copper foil, cobalt alloys layer containing at least one of nickel, phosphorus, zinc, and copper is superior in drilling property by laser.
In the case of a nickel layer alone, the laser drilling rate is low as compared with that by the present invention, and even if the amount of nickel is increased, the drilling rate cannot be improved. The layer is thus unsuitable as a layer (coating layer) for improving the laser drilling property.
Incidentally, the drilling rates were 0%, 2%, 67%, 73%, 68%, and 71% in the case where the nickel deposition amount at 32 mJ/pulse was 3,400 xcexcg/dm2, 6,100 xcexcg/dm2, 13,400 xcexcg/dm2, 20,333 xcexcg/dm2, 53,600 xcexcg/dm2, and 81, 333 xcexcg/dm2, respectively, and even when the nickel deposition amount was increased further, the drilling rate was hardly increased.
However, in the case where a nickel layer containing any one or more of copper, zinc, and phosphorus, that is nickel alloys layer containing these elements, is formed, the drilling rate can be improved approximately to the same level as that of the foregoing indium, tin, cobalt, zinc or cobalt alloy layer and more excellent laser drilling property can be achieved than that in the case of a layer of nickel alone. Consequently, the present invention includes the forgoing nickel alloy layer.
By the way, in the case of a low drilling rate as described above, it is of course possible to increase the drilling rate by heightening the laser output (energy) at the time of forming a hole.
However, if the laser energy is increased unnecessarily, a resin part of a board (copper-clad laminated board) is considerably damaged and it occurs that the hole diameter of the resin becomes wider than the diameter of a hole of a copper foil (layer)
If a hole of a resin is widened as described, the quality of a hole formed by laser is deteriorated including occurrence of detachment of the resin from the copper foil (layer) in the bottom part of the hole and further strict control of treatment conditions is required to prevent such quality deterioration, resulting in a big problem such as complication of processes and treatment operation.
Hence, it is generally better to carry out drilling efficiently with laser while laser energy is lowered as much as possible.
In terms of above described explanation, in the case of using common laser energy, the foregoing layer of nickel alone with a low drilling rate is not appropriate for a layer (coating layer) to improve the drilling property.
After plating treatment, stabilizer treatment with chromium and/or zinc may be carried out. Technique for the stabilizer treatment or a treatment liquid is not specifically limited. The stabilizer treatment may be carried out on the surface subjected to the foregoing plating treatment, that is, either partly on the face of a copper layer to which laser beams is radiated or on the whole surface of a copper foil.
As described above, the stabilizer treatment is naturally required not to deteriorate the characteristic properties of a copper foil to be employed for a circuit board and the stabilizer treatment of the present invention sufficiently satisfies those conditions. The stabilizer treatment scarcely affects the laser drilling property.
The following plating treatment methods are applicable for formation of a layer containing any one or more substances selected from indium, tin, cobalt, zinc, cobalt alloys and nickel alloys on the face to be radiated with laser beams in the present invention. The following are representative examples. The plating treatment methods described below are only kinds of preferable examples and the present invention is not at all restricted within those examples.
(Cobalt Plating Treatment)
Co concentration: 1 to 30 g/L,
Electrolytic solution temperature: 25 to 60xc2x0 C., pH: 1.0 to 4.0, current density: 0.5 to 5 A/dm2, Plating time: 0.5 to 4 seconds.
(Tin Plating Treatment)
Sn concentration: 5 to 100 g/L, sulfuric acid: 40 to 150 g/L
Electrolytic solution temperature: 25 to 40xc2x0 C., pH: 1.0 to 4.0, current density: 1.0 to 5 A/dm2, Plating time: 0.5 to 4 seconds.
(Indium Plating Treatment)
In concentration: 10 to 50 g/L, Sulfuric acid: 10 to 50 g/L
Electrolytic solution temperature: 20 to 40xc2x0 C., pH: 1.0 to 4.0, Current density: 1.0 to 20 A/dm2, Plating time: 0.5 to 4 seconds.
(Zinc-Cobalt Plating Treatment)
Zn concentration: 1 to 20 g/L, Co concentration: 1 to 30 g/L
Electrolytic solution temperature: 25 to 50xc2x0 C., pH: 1.5 to 4.0, Current density: 0.5 to 5 A/dm2, Plating time: 1 to 3 seconds.
(Copper-Nickel Plating Treatment)
Cu concentration: 5 to 20 g/L, Ni concentration: 5 to 20 g/L
Electrolytic solution temperature: 25 to 50xc2x0 C., pH: 1.0 to 4.0, Current density: 10 to 45 A/dm2, Plating time: 1 to 3 seconds.
(Copper-Cobalt Plating Treatment)
Cu concentration: 5 to 20 g/L, Co concentration: 5 to 20 g/L
Electrolytic solution temperature: 25 to 50xc2x0 C., pH: 1.0 to 4.0, Current density: 10 to 45 A/dm2, Plating time: 1 to 3 seconds.
(Zinc-Nickel Plating Treatment)
Zn concentration: 1 to 10 g/L, Ni concentration: 10 to 30 g/L
Electrolytic solution temperature: 40 to 50xc2x0 C., pH: 3.0 to 4.0, Current density: 0.5 to 5 A/dm2, Plating time: 1 to 3 seconds.
(Cobalt-Nickel Plating Treatment)
Co concentration: 5 to 20 g/L, Ni concentration: 5 to 20 g/L
Electrolytic solution temperature: 20 to 50xc2x0 C., pH: 1.0 to 4.0, Current density: 0.5 to 10 A/dm2, Plating time: 1 to 180 seconds.
(Copper-Cobalt-Nickel Plating Treatment)
Co concentration: 1 to 15 g/L, Ni concentration: 1 to 15 g/L, Cu concentration: 5 to 25 g/L
Electrolytic solution temperature: 25 to 50xc2x0 C., pH: 1.0 to 4.0, Current density: 1.0 to 30 A/dm2, Plating time: 1 to 180 seconds.
(Copper-Phosphorus Plating Treatment)
Co concentration: 5 to 20 g/L, P concentration: 1 to 30 g/L
Electrolytic solution temperature: 20 to 50xc2x0 C., pH: 1.0 to 4. 0, Current density: 0.5 to 15 A/dm2, Plating time: 1 to 180 seconds.
(Nickel-Phosphorus Plating Treatment)
Ni concentration: 5 to 20 g/L, P concentration: 1 to 30 g/L
Electrolytic solution temperature: 20 to 50xc2x0 C., pH: 1.0 to 4.0, Current density: 0.5 to 15 A/dm2, Plating time: 1 to 180 seconds.
The following plating treatment is applicable to the stabilizer treatment of the present invention. The following is a representative example. The stabilizer treatment described below is only one of preferable examples and the present invention is not restricted to the example.
(Chromium Stabilizer treatment)
K2Cr2O7 (Na2Cr2O7 or CrO3): 2 to 10 xcexcg/L,
NaOH or KOH: 10 to 50 g/L,
ZnO or ZnSO4-7H2O: 0.05 to 10 g/L,
pH: 3.0 to 4.0, Electrolytic solution temperature: 20 to 80xc2x0 C.,
Current density: 0.05 to 5 A/dm2, Plating time: 5 to 30 seconds.